Over the past two decades wireless technology has extended telephonic, and data communications to an unprecedented number of persons. Wireless satellite communication is an important means of communication in undeveloped regions of the world that are without an extant communication infrastructure. Satellite communication is invaluable for a variety of user groups such as disaster relief workers, geological prospectors and military personal.
Certain types of communications, such as video telephony, or the transfer of large data sets can benefit from high data rates. A directional antenna incorporated into a user's satellite communication terminal could in principle be of benefit for higher data rate communication because a directional antenna increases the link budget and thus allows a greater information symbol (e.g., bit) rate to be sustained within a prescribed transmitter power limit.
A problem with using a directional antenna instead of a fixed pattern, low gain (e.g., omnidirectional) antenna is that when a terminal equipped with a directional antenna is turned on there is in many cases no a priori knowledge of the correct pointing direction to the satellite and unlike a low gain antenna the directional antenna must be pointed (within a certain tolerance) toward the satellite in order to sustain communications with the satellite.
A phased array antenna is a type of directional antenna with no moving parts—it is steered electronically. Without the need for mechanisms to adjust the azimuth and zenith of the pointing directions, phased array antennas can generally be made smaller and lighter.
The capacity of a satellite system can be increased by defining multiple channels using one or more channel discriminators such as frequency, time slot and channel defining code. If a phased array antenna system were to be used in a system with a large number channels, the signal acquisition time would be greatly increased because a receiver would need to check each channel discriminator for each of many beam directions of the phased array antenna.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.